Annular divided wall column

ABSTRACT

An annular divided wall column is provided. The annular divided wall column includes a first annular column wall and a second annular column wall disposed within the first annular column wall and radially spaced therefrom to define an annulus column region as the space between the first annular column wall and the second annular column wall. An interior core column region is also defined by the interior space of the second annular column wall. The present annular divided wall column further includes a plurality of packing elements, disposed within the interior core column region within the annulus column region having different surface area densities and optionally, also have different geometries.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/042,189 filed on Jul. 23, 2018 that claims thebenefit of and priority to U.S. Provisional Patent Application Ser. No.62/550,262 filed on Aug. 25, 2017, the disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to annular divided wall columns for thecryogenic distillation of air or constituents of air. More particularly,the present invention relates to an annular divided wall column thatincludes an annulus column region defined as the space between a firstannular column wall and a second annular column wall and an interiorcore column region defined as the interior space of the second annularcolumn wall with a plurality of packing elements or trays disposedwithin the interior core column region and the annulus column region.

BACKGROUND

A major capital expense of a rectification plant for the separation ofair into components based on their relative volatility is the cost ofthe column casing and the space required for the column. This isparticularly the case where two or more columns are required to conductthe separation. Such multi-column systems are often used in cryogenicrectification, such as in the cryogenic rectification of air, wherecolumns may be stacked vertically or located side by side. It would behighly desirable to have a system which will enable rectification to becarried out with reduced column cost and with reduced space requirementsfor the columns.

Divided-wall columns have been proposed in the literature as a means tobetter utilize a given column diameter, and thereby reduce the capitalcost associated with construction of a plant to facilitate theseparation process. Divided-wall columns essentially contain multipledistillation sections at the same elevation within a single columnshell. An early example of the use of a divided-wall column is disclosedin U.S. Pat. Nos. 5,946,942 and 6,023,945 (Wong, et al.) discloses anapplication of divided-wall principles to air separation. These priorart systems disclose an apparatus wherein the lower pressure columncontains an inner annular wall. The region contained between the innerannular wall and the outer shell of the lower pressure columnconstitutes a section for the production of argon product. A drawback ofthe prior art divided-wall column structures includes maldistribution ofvapor within the annular divided wall columns separation sections aswell as maldistribution of the down-flowing liquids due to the largewall surface area, especially if the separation sections use structuredpacking as the mass-transfer elements.

Accordingly it is an object of this invention to provide a column systemfor rectification of air which has reduced costs and space requirementsover conventional air separation column systems and that overcomes thedifficulties and disadvantages of the prior art annular divided wallcolumns to provide better and more advantageous performance.

SUMMARY OF THE INVENTION

The present invention may be characterized as an annular columncomprising: (i) a first annular column wall; (ii) a second annularcolumn wall radially spaced from the first annular column wall anddisposed within a first interior space of the first annular column wallto define an annulus column region between the first annular column walland the second annular column wall and to define an interior core columnregion as part or all of a second interior space of the second annularcolumn wall; (iii) a plurality of structured packing elements of a firsttype disposed within the annulus column region; and (iv) a plurality ofstructured packing elements of a second type disposed within theinterior core column region, wherein the first type of structuredpacking elements and the second type of structured packing elements havedifferent surface area densities.

In some embodiments of the present annular divided wall column, thefirst type of structured packing elements and the second type ofstructured packing elements may also have different geometries, and inparticular different nominal inclination angle of corrugations to thehorizontal axis.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims distinctly pointing outthe subject matter that applicants regard as their invention, it isbelieved that the invention will be better understood when taken inconnection with the accompanying drawings in which:

FIG. 1 is a top section view of an annular divided wall column inaccordance with one embodiment of the present invention;

FIG. 2 is a top section view of an annular divided wall column inaccordance with another embodiment of the present invention;

FIG. 3 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 4 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 5 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 6 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 7 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 8 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 9 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 10 is a top section view of an annular divided wall column inaccordance with yet another embodiment of the present invention;

FIG. 11 is a side section, cut-away view of a two-column divided wallarrangement in accordance with an embodiment of the present invention;

FIG. 12 is a side section, cut-away view of a two-column divided wallarrangement in accordance with another embodiment of the presentinvention;

FIG. 13 is a side section, cut-away view of an annular divided wallcolumn in accordance with one or more embodiments of the presentinvention;

FIG. 14 is a side section, cut-away view of an annular divided wallcolumn in accordance with further embodiments of the present invention;

FIG. 15 is a side section, cut-away view of an annular divided wallcolumn in accordance with still further embodiments of the presentinvention;

FIG. 16 is a top section view of a three-column divided wall arrangementin accordance with an embodiment of the present invention;

FIG. 17 is a side section, cut-away view of the three-column dividedwall arrangement of FIG. 13;

FIG. 18 is a top section view of another three-column divided wallarrangement in accordance with an embodiment of the present invention;

FIG. 19 is a side section, cut-away view of the three-column dividedwall arrangement of FIG. 15;

FIG. 20 is an isometric view of a ring tray suitable for use in one ormore embodiments of the present annular divided wall column;

FIG. 21 is an isometric view of a horseshoe tray suitable for use in oneor more embodiments of the present annular divided wall column;

FIG. 22 is an isometric view of a parallel flow tray suitable for use inone or more embodiments of the present annular divided wall column;

FIGS. 23a and 23b are isometric views of two-pass crossflow trayssuitable for use in one or more embodiments of the present annulardivided wall column;

FIG. 24 is an isometric view of a two-pass parallel flow tray suitablefor use in one or more embodiments of the present annular divided wallcolumn;

FIG. 25 is an isometric view of a multiple downcomer tray suitable foruse in one or more embodiments of the present annular divided wallcolumn;

FIG. 26 is a isometric view of a type of arcuate wedge or curved packingsuitable for use in one or more embodiments of the present annulardivided wall column;

FIGS. 27a, 27b, and 27c are perspective views of various types of randompacking suitable for use in one or more embodiments of the presentannular divided wall column;

FIG. 28 is a side section view of an annular divided wall column inaccordance with one or more embodiments of the present invention;

FIG. 29 is a side section view of an annular divided wall column inaccordance with various embodiments of the present invention;

FIG. 30 is a side section view of an annular divided wall column inaccordance with further embodiments of the present invention; and

FIG. 31 is a side section view of an annular divided wall column inaccordance with still further embodiments of the present invention.

DETAILED DESCRIPTION

The following paragraphs include detailed descriptions of variousembodiments of the present annular divided wall column for the cryogenicrectification of air, including descriptions of: (i) annular dividedwall column structures; (ii) process and/or service arrangements for thedifferent regions within the annular divided wall column; and (iii)arrangements of mass transfer elements within the annular divided wallcolumn.

Annular Divided Wall Column Structures

As seen in the FIGS. 1 through 10, embodiments of the present annulardivided wall column 10 include a first annular column wall 12 and thesecond annular column wall 16 that may be concentrically disposedrelative to one another as shown in FIGS. 1 through 8 or may beeccentrically disposed relative to one another as shown in FIGS. 9 and10. As further shown in the drawings, the first annular column wall 12may have a cylindrical configuration with a cross section that iscircular (See FIGS. 1 through 6) or elliptical configuration (See FIGS.7 and 8) and the second annular column wall 16 may also have across-section configuration that is circular (See FIGS. 1 through 5, 8,and 9) or elliptical (See FIGS. 6, 7, and 10).

Examples of different arrangements of mass transfer elements and otherdevices employed within the present annular divided wall column aregenerally depicted in FIGS. 1 through 10 where structured packingelements are shown as hatched sections and trays are depicted as shadedsections.

In FIG. 1 and FIG. 6, the annulus column region 14 preferably containsstructured packing as well as the associated collectors, distributors,support structures, caps and piping while the interior core columnregion 18 also contains structured packing and the associatedcollectors, distributors, support structures, caps and piping. Thesurface area density and/or geometry of the structured packing elementsin the annulus column region 14 may be the same as or different than thesurface area density and/or geometry of the structured packing elementsin the interior core column region 18.

In FIG. 2, FIG. 8 and FIG. 9, the annulus column region 14 preferablycontains a plurality of structured packing elements as well as theassociated collectors, distributors, support structures, caps, andpiping while the interior core column region 18 preferably includes aplurality of trays. Similarly, FIG. 3, FIG. 7, and FIG. 10 showembodiments of the annular divided wall column 10 wherein the annuluscolumn region 14 preferably contains structured packing elements as wellas the associated collectors, distributors, support structures, caps,and piping while the interior core column region 18 preferably includesa heat exchange device 20, a phase separator device and/or one or moreconduits for the movement of liquids and/or vapors within the column.

In FIG. 4, the annulus column region 14 preferably contains a pluralityof trays while the interior core column region 18 preferably containstrays and one or more beds of structured packing elements as well as theassociated collectors, distributors, support structures, caps, andpiping. In FIG. 5, the annulus column region 14 preferably contains oneor more beds of structured packing elements as well as the associatedcollectors, distributors, support structures, and piping while theinterior core column region 18 preferably contains trays and one or morebeds of structured packing elements as well as the associatedcollectors, distributors, support structures, caps, and piping.

Turning now to FIGS. 11 through 15, there is shown selected embodimentsof a two-column annular divided wall arrangement 100 for the cryogenicrectification of air, and having two concentric annular column walls.The first annular column wall 112 is preferably formed by the exteriorshell of the air separation column structure such while the secondannular column wall 116 extends over only a portion or section of theentire exterior column shell and is preferably disposed within theexterior shell of the air separation column structure. In suchtwo-column divided wall arrangements, the vertical height of the firstannular column wall 112 is preferably greater than a vertical height ofthe second annular column wall 116.

In FIG. 11, the interior core column region 118 contains one bed ofstructured packing elements 125 along with a collector 135 anddistributor 145 while the annulus column region 114 also contains onebed of structured packing 155 along with an associated collector 165 anddistributor 175. FIG. 12 depicts an embodiment where the interior corecolumn region 118 contains a plurality of trays 150 while the annuluscolumn region 114 also contains multiple beds of structured packingelements 155A, 155B along with an associated collectors 135 anddistributors 145. FIG. 13 depicts an embodiment where the interior corecolumn region 118 contains one bed of structured packing elements 125Calong with the associated collector 135 and distributor 145 as well as aheat exchange device 120 such as an argon condenser while the annuluscolumn region 114 also contains multiple beds of structured packingelements 155A, 155B along with an associated collectors 165 anddistributors 175. FIG. 14 depicts yet another embodiment where theinterior core column region 118 contains one bed of structured packingelements 125 along with the associated collector 135 and distributor 145as well as a plurality of trays 150 while the annulus column region 114also contains one bed of structured packing elements 155 along with theassociated collector 165 and distributor 175 as well as a plurality oftrays 180. Lastly, FIG. 15 depicts still another embodiment where theinterior core column region 118 contains one or more beds of structuredpacking elements 125 along with the associated collector 135 anddistributor 145 as well as a plurality of trays 150 while the annuluscolumn region 114 contains multiple beds of structured packing elements155A, 155B along with an associated collectors 165 and distributors a75.

In the illustrated two-column divided wall arrangements, a cap or header190 may be employed to partially enclose either the annulus columnregion 114 or the interior core column region 118. To partially enclosethe annulus column region 114, a cap or header 190 is placed above theannulus column region that extends from the top of the second annularcolumn wall 116 to an intermediate location of the first annular columnwall 112. To partially enclose the interior core column region, a cap orheader is attached to the top of the second annular column wall 116 tocover the interior core column region 118.

Turning now to FIGS. 16 and 17, there is shown an embodiment of athree-column divided wall arrangement 200 having three concentric oreccentric annular column walls. In the preferred configuration of thethree-column divided wall arrangement 200, the first annular column wall212 may be defined as the main shell of the air separation columnstructure. The second annular column wall 216 is disposed within thefirst annular column wall and a third column wall 217 is placed ordisposed exterior to the first annular column wall 214. In thisthree-column divided wall arrangement, the third column wall 217 isradially spaced from the first annular column wall 212 and surrounds orpartially surrounds the first annular column wall to define an outercolumn region 219 between the first annular column wall 212 and thethird column wall 217. As with the two-column divided wallconfiguration, the vertical height of the third column wall 217 ispreferably less than the vertical height of the first annular columnwall 212 to form a lower height bubble or blister section to theexterior column shell.

In this three-column divided wall arrangements, an outer cap 222 orouter header covering the outer column region 219 is provided. Suchouter cap 222 or outer header preferably extends from the top of thethird column wall 217 to an intermediate location of the first annularcolumn wall 212 to partially enclose the outer column region 219.

In FIG. 16 and FIG. 17, the outer column region 219 preferably definesor includes one or more conduits 290 for the movement of vapors and/orliquids within the column while the inner annulus column region 216preferably contains one or more beds of structured packing elements255A, 255B as well as the associated collectors 265, distributors 275,support structures, and piping. The interior core column region 218preferably includes one or more beds of structured packing elements225A, 225B as well as the associated collectors 235, distributors 245,support structures, caps, and piping. Optionally, the interior corecolumn region 218 may also contain a plurality of trays and/or a heatexchange device disposed toward the lower section of the interior corecolumn regions or even below the bottom of the annulus column region. Aswith the above-described embodiments, the surface area densities and/orgeometries of the structured packing beds in the annulus column regionmay be the same as or different than the surface area densities and/orgeometries of the structured packing beds in the interior core columnregion or in the other beds of the annulus column region.

While the outer column region 219 of FIGS. 16 and 17 are shown havingone or more conduits 290 for the movement of vapors and/or liquids to,from, or within the column structures, it is contemplated that the outercolumn region 219 may alternatively be designed for mass transfer byemploying structured packing and/or trays. Likewise, while the interiorcore column region 218 of FIGS. 16 and 17 are shown having one or morebeds of structured packing elements, it is further contemplated thatvarious embodiments may also include trays in addition to or in lieu ofthe structure packing elements or even other devices or conduits.

An alternate embodiment of the three-column divided wall arrangements isshown in FIGS. 18 and 19. In this embodiment of the three-column dividedwall arrangement, the first annular column wall 252 may be defined asthe main shell of the air separation column structure and the secondannular column wall 256 is disposed concentrically or eccentricallywithin the first annular column wall 252. A third column wall 257 isplaced within interior space defined by the second annular column wall256 and divides or segments the interior space into two separateregions, namely a first core interior region 260 and a second coreinterior region 270.

In FIGS. 18 and 19, the first core interior region 260 preferablydefines or includes a heat exchange device 280, a phase separator deviceand/or one or more conduits for the movement of vapors and/or liquidswithin the column while the second core interior region 270 preferablycontains one or more beds of structured packing elements 225A, 225B aswell as the associated collectors 235, distributors 245, supportstructures, and piping and/or a plurality of trays. The annulus columnregion 254 preferably includes one or more beds of structured packingelements 255A, 255B as well as the associated collectors 265,distributors 275, support structures, caps, and piping. Again, thesurface area densities and/or geometries of the structured packing bedsin the annulus column region may be the same as or different than thesurface area densities and/or geometries of the structured packing bedsin the interior core column region or in the other beds of the annuluscolumn region.

In some embodiments, it may be advantageous to apply a high flux coatingor porous coating to an interior surface of the first annular columnwall or third annular column wall. Similarly, a high flux coating orporous coating may also be applied to a surface of the second annularcolumn wall, preferably the surface exposed to the colder fluid. As usedherein, the terms ‘high-flux coating’ and ‘porous coating’ refers tothose coatings that by virtue of its built-in porosity enhance boilingby providing so-called nucleation sites. The porous coating providesmicro-scale cavities that have the effect of increasing the number ofnucleation sites and bubble departure frequency per site. As a result,the boiling rate can be enhanced. Examples of such high flux coatings orporous coatings are described in U.S. Patent Application PublicationNos. 2017/0108148 and 2017/0108296, the disclosures of which areincorporated by reference.

In other embodiments, the interior surface of the first annular columnwall, interior surface of the first annular column wall, or one or moresurfaces of the second annular column wall may also include surfacetexturing. The term “surface texturing”, as used herein, is to beunderstood as denoting any roughening, grooving, fluting, or otherwiseforming or impressing a geometric pattern on the wall surface.

Process/Service Arrangements in an Annular Divided Wall Column

In some embodiments, the annular column region is designed or configuredfor rectification of an argon-oxygen containing stream to separate theargon-oxygen containing stream into an argon-rich overhead stream and anoxygen-rich stream. In other embodiments, the annular column region isdesigned or configured for rectification of a nitrogen-oxygen containingstream to separate the nitrogen-oxygen containing stream into a nitrogenrich overhead stream and an oxygen-rich stream.

Similarly, the interior core column region is designed or configured forrectification of an argon-oxygen containing stream to separate theargon-oxygen containing stream into an argon-rich overhead stream and anoxygen-rich stream. In other embodiments, the interior core columnregion is designed or configured for rectification of a nitrogen-oxygencontaining stream to separate the nitrogen-oxygen containing stream intoa nitrogen rich overhead stream and an oxygen-rich stream.

In yet other embodiments, the annular column region may be designed orconfigured for rectification of a nitrogen-oxygen containing stream toseparate the nitrogen-oxygen containing stream into a first nitrogenrich overhead stream and a first oxygen-rich stream of a first purityand the interior core column region may be designed or configured forrectification of another nitrogen-oxygen containing stream to separateit into a second nitrogen rich overhead stream and a second oxygen-richstream of a second purity. Alternatively, the annular column region maybe designed or configured for rectification of a nitrogen-oxygencontaining stream to separate the nitrogen-oxygen containing stream intoa first nitrogen rich overhead stream of a first purity and a firstoxygen-rich stream while the interior core column region may be designedor configured for rectification of another nitrogen-oxygen containingstream to separate it into a second nitrogen rich overhead stream of asecond purity and a second oxygen-rich stream.

Other contemplated process or service arrangements for the annulardivided wall column include disposing a heat exchange device or a phaseseparator device within the interior core column region. The heatexchange device disposed in the interior core column region ispreferably either: (i) an argon condenser configured to condense anargon-rich stream for use as a reflux stream, or a liquid argon productstream; (ii) a main condenser-reboiler configured to condense anitrogen-rich stream for use as a reflux stream or a liquid nitrogenproduct stream; or (iii) a subcooler configured to subcool anitrogen-rich liquid stream, an oxygen rich liquid stream, or a liquidair stream for use in the cryogenic air separation plant. In embodimentswhere a phase separator device is disposed in the interior core columnregion, the phase separator is preferably configured to separate atwo-phase oxygen-containing stream into an oxygen containing liquidstream and an oxygen containing vapor stream.

Still other contemplated process or service arrangements for the annulardivided wall column include using the outer column region in athree-column divided wall arrangement as a vapor conduit or disposingone or more vapor conduits within outer column region in a three-columndivided wall arrangement that is configured to direct one or morestreams to selected locations in the annular column region or theinterior core column region.

Mass Transfer Elements in an Annular Divided Wall Column

Turning now to FIGS. 20 through 25, the plurality of mass transfercontacting elements disposed within the annulus column region orinterior core column region can be trays, packing or combinationsthereof. Where trays are employed in the interior core region of theannular divided wall column, suitable types of trays include: ring trays310 of the type generally shown in FIG. 20; horseshoe trays 320 of thetype shown in FIG. 21; single pass cross flow trays; parallel flow trays330 of the type shown in FIG. 22; two pass crossflow trays 340 of thetype shown in FIGS. 23a and 23b ; two pass parallel flow trays 350 ofthe type shown in FIG. 24; or multiple downcomer trays 360 of the typeshown in FIG. 25. Where trays are employed in the annulus column regionof the annular divided wall column, suitable types of trays includeannular cross flow trays or annular parallel flow trays.

Where packing is employed in either the annulus column region or theinterior core column region of the annular divided wall column, possiblecolumn packing arrangements include structured packing, strip packing,random packing, or even silicon carbide foam packing, as described inmore detail below. Such packing arrangements would further include aplurality of liquid distributors, collectors, or combinedcollector-distributor devices of the type shown and described in U.S.Pat. Nos. 9,004,460 and 9,457,291, incorporated by reference herein. Thepreferred embodiments include structured packing as such arrangementsadvantageously provide lower pressure drop, higher efficiency, highercapacity; and reduced liquid hold-up compared to trays and randompacking. However, structured packing is prone to liquid maldistribution.

Structured packing is generally formed from corrugated sheets ofperforated embossed metal or plastic, or wire gauze. The resultingstructure is a very open honeycomb-like structure with inclined flowchannels of the corrugations giving a relatively high surface area butwith very low resistance to gas flow. In applications using structuredpacking, the structured packing is preferably constructed of materialsselected from the group consisting of: aluminum sheet metal, stainlesssteel sheet metal, stainless steel gauze, copper and plastic. Thesurfaces of the structured packing may be smooth or may include surfacetexturing such as grooving, fluting, or patterned impressions on thesurfaces of the structured packing sheets. Examples of the preferredtypes of structured packing are shown and described in U.S. Pat. Nos.5,632,934 and 9,295,925; the disclosures of which are incorporated byreference herein.

The size or configuration of structure packing is broadly defined by thesurface area density of the packing and the inclination angle of thecorrugated flow channels in the main mass transfer section of thestructured packing. The preferred density of the structured packing isbetween about 100 m²/m³ to 1200 m²/m³ and more preferably are selectedfrom the group of commercially available structured packing havingsurface area densities of 110 m²/m³; 220 m²/m³; 250 m²/m³; 350 m²/m³;430 m²/m³; 500 m²/m³; 730 m²/m³; 950 m²/m³; and 1200 m²/m³. The geometryof the structure packing, as characterized by the inclination angle ofthe corrugated flow channels in the main mass transfer section of thestructured packing, preferably includes a nominal inclination angle tothe horizontal axis of between about 35° to 70°, which encompassesX-size packing (i.e. nominal inclination angle of about 60°), Y-sizepacking (i.e. nominal inclination angle of about 45°); and Z-sizepacking (i.e. nominal inclination angle of about 40°).

In some embodiments, the structured packing configuration for theannulus column region of the annular divided wall column are a pluralityof curved or arcuate wedge shaped bricks 375 or curved bricks, shown inFIG. 26. Alternatively, the structured packing for the annulus columnregion may be configured as a donut shaped disk or as conventionalrectangular bricks. Although the curved or arcuate wedge shapedstructured packing bricks can also be used in the interior core columnregion, the preferred structured packing configuration for the interiorcore column region are round disks (e.g. pancake packing) orconventional rectangular bricks. The preferred height of the disksand/or bricks is between about 10 and 12 inches, although half-heightbricks of 5 inches to 6 inches may also be used. Also, packings withhigher pour point densities or drip point densities are often preferredfor use in the annulus column region.

Alternatively, structured packing made of silicon carbide may be used inselected applications. Such silicon carbide or other foam like materialpacking is generally described in U.S. Pat. No. 9,375,655; while inapplications using strip packing, the preferred arrangement is similarto that disclosed in U.S. Patent Application Publication No.2016/0061541. Both disclosures are incorporated by reference herein.

In applications using random packing, the preferred types of randompacking elements include proprietary packing selected from the groupconsisting of: Berl Saddle packing; Rashig Ring packing; Pall® Ringpacking; Intalox® Saddle packing; Intalox® Metal Tower Packing (IMTP®);Cascade® MiniRing (CMR®) packing; Nutter Ring® packing; or othercommercially available random packing. Such random packing elementspreferably have a nominal piece size ranging from about 15 mm to about100 mm. Examples of several types of random packings 390A, 390B, 390Care shown in FIG. 27.

Examples of different arrangements of structured packing employed withinthe present annular divided wall column are generally illustrated inFIGS. 28 through 31 and described in the paragraphs that follow. In someembodiments of the annular divided wall column arrangement 400, aplurality of structured packing elements of a first type 455A aredisposed within the annulus column region and a plurality of structuredpacking elements of a second type 425B are disposed within the interiorcore column region, wherein the first type of structured packingelements 455A and the second type of structured packing elements 425Bhave different surface area densities. For example, the structuredpacking elements disposed within the annulus column region may havesurface area densities of between about 700 to 1000 m²/m³ whereas thestructured packing elements disposed within the interior core columnregion may have surface area densities of between about 400 to 700m²/m³.

Similarly, a plurality of structured packing elements of a first type455A are disposed within the annulus column region and a plurality ofstructured packing elements of a second type 425B are disposed withinthe interior core column region, wherein the first type of structuredpacking elements 455A and the second type of structured packing elements425B have different geometries. For example, the structured packingelements disposed within the annulus column region may have a nominalinclination angle to the horizontal axis of about 55° to 70° to minimizewall flow whereas the structured packing elements disposed within theinterior core column region may have a nominal inclination angle to thehorizontal axis of about 45° to 55°.

In other embodiments, the structured packing elements in either theinterior core column region or the annulus column region may comprisetwo or more beds of structured packing. In addition, where multiple bedsof structured packing are employed in either region, the adjacent bedsmay have different surface area densities and/or different geometries.For example, a first bed of structured packing elements 425C of a firstsurface area density may be disposed within the interior core columnregion while a second bed structured packing elements 425D of a secondsurface area density is also disposed within the interior core columnregion above or below the first bed of structured packing elements 425Cof the first surface area density. In such example, the first bed ofstructured packing elements 425C disposed within the interior corecolumn region may have a surface area density of between about 400 to700 m²/m³ whereas the second bed of structured packing elements 425Ddisposed within the interior core column region may have a surface areadensity of between about 700 to 1000 m²/m³.

Likewise, a first bed of structured packing elements 455E having a firstsurface area density is disposed within the annulus column region whilea second bed structured packing elements 455F having a second surfacearea density may be disposed within the annulus column region above orbelow the first bed of structured packing elements 455E. In thisexample, the first bed of structured packing elements 455E disposedwithin the annulus column region may have a surface area density of 700m²/m³ or less whereas the second bed of structured packing elements 455Fdisposed within the annulus column region may have a surface areadensity of about 700 to 1200 m²/m³.

Still further, a first bed of structured packing elements 455G having afirst geometry or density may be disposed within the annulus columnregion while a second bed of structured packing elements 455H having asecond geometry or density is also disposed within the annulus columnregion above or below the first bed of structured packing elements 455G.For example, the first bed of structured packing elements 455G disposedwithin the annulus column region may have a nominal inclination angle tothe horizontal axis of about 55° to 70° whereas the second bed ofstructured packing elements 455H disposed within the annulus columnregion may have a nominal inclination angle to the horizontal axis ofabout 45° to 55°. Similarly, the first bed of structured packingelements 425J having a first geometry or density may be disposed withinthe interior core column region while the second bed of structuredpacking elements 425K having a second geometry or density is alsodisposed within the interior core column region above or below the firstbed of structured packing elements. An example would be wherein thefirst bed of structured packing elements 425J may have a nominalinclination angle to the horizontal axis of about 55° to 70° while thesecond bed of structured packing elements 425K may have a nominalinclination angle to the horizontal axis of about 30° to 55°.

Certain preferred embodiments employ a combination of structured packingelements and trays. For example, a plurality of structured packingelements may be disposed within the interior core column region and aplurality of trays is also disposed within the interior core columnregion above and/or below the structured packing elements. In suchembodiments, the structured packing elements disposed within theinterior core column region may have a surface area densities of betweenabout 100 m²/m³ to 1200 m²/m³ and a nominal inclination angle to thehorizontal axis of between about 35° to 70°, while the plurality oftrays may be selected from the group consisting of: ring trays;horseshoe trays; parallel flow trays; two pass crossflow trays; two passparallel flow trays; multiple downcomer trays; or combinations thereof.

While the present invention has been characterized in various ways anddescribed in relation to the preferred structural embodiments and/orpreferred methods, there are numerous additions, changes andmodifications that can be made to the disclosed structures and methodswithout departing from the spirit and scope of the present invention asset forth in the appended claims. For example, while the present annulardivided wall column has been shown and described as suitable for use inthe cryogenic rectification of air or constituents of air in an airseparation unit, it is fully contemplated that such annular divided wallcolumn arrangements may also be suitable for the separation orpurification of other industrial gases including off-gases or tail gasesof various industrial processes.

We claim:
 1. An annular divided wall column comprising: a first annularcolumn wall; a second annular column wall radially spaced from the firstannular column wall and disposed within a first interior space of thefirst annular column wall to define an annulus column region between thefirst annular column wall and the second annular column wall and todefine an interior core column region as part or all of a secondinterior space of the second annular column wall; a plurality ofstructured packing elements of a first type disposed within the annuluscolumn region; and a plurality of structured packing elements of asecond type disposed within the interior core column region; wherein thefirst type of structured packing elements and the second type ofstructured packing elements have different surface area densities andthe surface area densities of the first type of structured packingelements and the second type of structured packing elements are bothgreater than about 100 m²/m³; and wherein the first type of structuredpacking elements has a first nominal inclination angle of corrugationsand the second type of structured packing elements have a second nominalinclination angle of corrugations that is different than the firstnominal inclination angle of corrugations to the horizontal axis, andwherein the nominal inclination angle of corrugations to the horizontalaxis for both the first type of structured packing elements and thesecond type of structured packing elements is between about 35° to 70 °.2. The annular divided wall column of claim 1, wherein the first annularcolumn wall and the second annular column wall are concentricallydisposed relative to one another.
 3. The annular divided wall column ofclaim 1, wherein the plurality of structured packing elements of thefirst type and of the second type are constructed of aluminum sheetmetal or stainless steel sheet metal.
 4. The annular divided wall columnof claim 1, wherein the structured packing elements of the first typeand of the second type are configured as rectangular bricks.
 5. Theannular divided wall column of claim 1, wherein the surface areadensities of the first type of structured packing elements and thesecond type of structured packing elements are selected from a groupconsisting of: 110 m²/m³; 220 m²/m³; 250m²/m³; 350m²/m³; 430 m²/m³; 500m²/m³; 730 m²/m³; 950m²/m³; and 1200m²/m³.
 6. The annular divided wallcolumn of claim 1, wherein the surface area density of the first type ofstructured packing elements is greater than or equal to about 700 m²/m³and the surface area density of the second type of structured packingelements is between about 100 m²/m³ and about 700 m²/m.
 7. The annulardivided wall column of claim 1, wherein the first nominal inclinationangle of corrugations to the horizontal axis is between about 50° to 70°and the second nominal inclination angle of corrugations to thehorizontal axis is between about 35° to 55 °.
 8. The annular dividedwall column of claim 1, wherein the first nominal inclination angle ofcorrugations to the horizontal axis and second the nominal inclinationangle of corrugations to the horizontal axis are selected from a groupconsisting of: 40° ; 45° ; 50° ; 55° ; and 60 °.